<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    body {
        margin: 0px;
        padding: 0px;
        font: 12px/1.5 tahoma,'\5FAE\8F6F\96C5\9ED1',sans-serif;
}


    .comm-topact {
    width: 100%;
    min-width: 1230px;
    height: 360px;
    overflow: hidden;
    position: relative;
    background: center top no-repeat;
    -webkit-transition: height .6s,background,.6s;
    transition: height .6s,background,.6s;
    
    }
    
.comm-topact.big {
    height: 720px!important;
}
    .topact-big-img, .topact-small-img {
        position: absolute;
        left: 50%;
        top: 0;
        width: 1920px;
        height: 100%;
        margin-left: -960px;
    }
    .topact-small-img {
    -webkit-transition: opacity .6s;
    transition: opacity .6s;
    opacity: 1;
}
</style>
<body>
    <div class="comm-topact big">
        <img class="topact-big-img" src="img/1.jpg">
        <img class="topact-small-img" src="img/1.jpg">
    </div>
</body>
</html>